<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .Grid {
            display: flex;
            background-color: red;
        }
        
        .Grid-cell {
            flex: 1;
        }
        
        .Grid-cell.u-full {
            flex: 0 0 100%;
        }
        
        .Grid-cell.u-1of2 {
            flex: 0 0 50%;
        }
        
        .Grid-cell.u-1of3 {
            flex: 0 0 33.3333%;
        }
        
        .Grid-cell.u-1of4 {
            flex: 0 0 25%;
        }
        /* 这个地方 不是很多理解 */
    </style>
</head>

<body>
    <div class="Grid">
        <div class="Grid-cell u-1of4">元素1</div>
        <div class="Grid-cell">元素2</div>
        <div class="Grid-cell u-1of3">元素3</div>
    </div>
</body>

</html>